1. Field of the Invention
This invention relates to a data storage medium, a method of manufacturing a data storage medium, and a tool for use in the method.
2. Description of the Prior Art
One class of data storage techniques comprises selectively irradiating the surface of a storage medium, the medium being such that, when irradiated at sufficient intensity and duration, its properties are altered in some manner which is readily detectable. In this way data can be written onto and read from the storage medium. The writing irradiation may be electromagnetic or particulate. The advantage of electromagnetic writing radiation is that the writing (recording) operation need not be carried out in vacuum, while that of particulate writing radiation is that for any specified resolution, or data packing density, the depth of focus is much greater than for electromagnetic writing radiation.
When electromagnetic writing radiation is used, one of the difficulties frequently encountered is that the proportion of the incident energy absorbed by the data recording and storage medium may be small, and the energy required to alter detectably its properties may be large. Either or both of these restrictions may increase the energy required to write a detectable data spot on the data storage medium, which can increase the cost of the radiator or slow down the writing speed, or both.
Strongly absorbent surfaces have been prepared by producing a surface which is rough on a microscopic scale and in which the depth of the texture is large compared with its pitch. Such a surface is described by Spiller et al in Applied Optics Vo. 19, No. 17, Sept. 1, 1980 pp 3022-3026. However, the methods so far known for the production of such surfaces, such as implantation and etching, are inherently expensive. Furthermore, surfaces made by etching techniques cannot easily be replicated because etch pits tend to include undercut areas and are often relatively deep.